This is a re-revised competitive renewal of a program project to investigate the cellular and molecular mechanisms underlying the pathogenicity of autoreactive T cells against myelin and the factors that drive T cells towards a pathogenic or disease protective phenotype. To address this theme, we propose to analyze two recently discovered molecular pathways in these cells: First we will analyze the role of newly discovered transcription factor, T-bet which is crucial for IFN-y production in the induction of pathogenic and inhibition of regulatory T cells. Second, we will analyze the expression and role of newly discovered family of cell surface molecules called TIMs (T cell Immunoglobulin and Mucin) that are differentially expressed on Thl and Th2 cells. Utilizing these two newly discovered molecular pathways, we propose to analyze the transcriptional basis for the generation of autopathogenic vs. regulatory T cells and identify cell surface markers that can be utilized to differentiate and modulate effector functions of these cells. To this end, four interdependent projects have been constructed which will utilize the EAE model and investigate immune responses in patients with multiple sclerosis. The projects led by Laurie Glimcher (Project 1), Vijay Kuchroo (Project 2), Howard Weiner (project 3) and David Hafler (project 4) are highly interdependent and address a common theme: an understanding of molecular mechanisms of generation of autopathogenic T cells that appear crucial in the induction of multiple sclerosis. The main themes of the PPG are as follows: 1. Study the role of T-bet transcription factor in the generation of pathogenic vs. regulatory T cells in CNS autoimmune disease (EAE and MS);2. Determine the role of TIM family of molecules that are differentially expressed on the surface of Thl and Th2 (and other) cells in the induction of autopathogenic and regulatory T cells;3.Understand the role of T-bet transcription factors and TIM molecules in the induction of mucosal and peripheral tolerance;and 4. Analyze whether T-bet and TIM molecules can define pathogenic and regulatory T cells in human MS patients as well. As outlined in the re-revised program project, investigation of basic mechanisms in animal models, immune responses in MS patients, and strategies to induce regulatory cells will provide a better understanding of basic and applied mechanisms required to reach the goal of developing effective therapy for multiple sclerosis.